Well known are internal combustion engines capable of switching depending on states, among plural kinds of fuel for use or changing a mixture ratio of a plural kinds of fuel. As a control device for such an internal combustion engine, there is known a control device which detects a combustion state has become an inappropriate state with a sensor and changes a mixture ratio or an ignition timing so that the combustion state changes from the inappropriate state to an appropriate state (Patent Literature 1). In addition, as an internal combustion engine capable of switching among plural kinds of fuel for use, there is known an internal combustion engine which switches, when it is determined that air pollutants reach a high density in exhaust air, to fuel having a little amount of air pollutants (Patent Literature 2).